Commercial processing of thermoplastic polymers, such as extrusion and molding, is well-known in the prior art and may be accomplished by a diverse variety of techniques. Generally, thermoplastic polymers have softening temperatures of about 130.degree. C. and higher and, therefore, require processing at temperatures significantly higher, such as 200.degree. C. and higher.
In the past, these 200.degree. C. and higher processing temperatures were of little concern because the necessary heat could be generated from a variety of heat sources and capital equipment. However, with the current worldwide energy shortage and the increasing concern related to the worker's environment, there is a need for a commercial process which permits high-softening temperature thermoplastic polymers to be processed at temperatures lower than those currently used. Such a lower processing temperature represents a significant reduction in energy used, a significant savings in energy costs and an improvement in the worker's environment since less heat is likely to be dissipated by the processing equipment.
Furthermore, it is desirable to prepare thermoplastic polymers which contain additives, such as chemical blowing agents, thermostabilizers, hydrolytic stabilizers, mold release agents, pigments, etc. which are molded or extruded at a later date or at a different site. When incorporating additives in such thermoplastic polymers, it is desirable to use as low a temperature as possible in order to minimize the heat histories of such additives and thermoplastic polymers in order to avoid deterioration of the physical, mechanical or chemical properties of the thermoplastic polymer or additives.
A severe problem currently exists in the preparation of a masterbatch or concentrate of a thermoplastic polymer intimately blended with a chemical blowing agent. It is often easier first to prepare such masterbatches or concentrates and then subsequently add them to a larger quantity of a compatible thermoplastic polymer. However, due to the processing temperature necessary to soften many thermoplastic polymers, a chemical blowing agent cannot be intimately blended with the polymer to form a concentrate without activating the chemical blowing agent. This problem, therefore, often requires the physical blending of such a chemical blowing agent with a thermoplastic polymer at the actual molding site making this molding step more expensive, cumbersome and difficult due to the powder form of many chemical blowing agents.
Thus, a real need exists for a process which permits high softening temperature, thermoplastic polymers to be processed at temperatures lower than those currently used.
In accordance with the present invention, a method is provided which permits high softening temperature, thermoplastic polymers to be processed at temperatures lower than those currently used. Novel chemical blowing agent concentrates are further provided.